1. Field of the Invention
This invention relates to new sweet, non-crystallizing syrups derived directly and solely from starch, containing maltulose, dextrose and levulose, plus, optionally, maltose and/or saccharides having degrees of polymerization (DP's) greater than 2, and to a process for making same.
2. The Prior Art
Maltulose (4-alpha-D-glucopyranosyl-D-fructose) is a ketose disaccharide which is present in honey; it can be synthesized by isomerizing maltose (the corresponding aldose) at an alkaline pH.
Until recently, there has been relatively little investigatory work conducted on the properties of maltulose. J. H. Pazur and K. Kleppe report that it is only slowly hydrolyzed by purified amylo-glucosidase. ("The Hydrolysis of Alpha-D-Glucosides by Amylo-Glucosidase from Aspergillus niger", The Journal of Biological Chemistry, Vol. 237, No. 4, Apr. 1962, pgs. 1002-1006.) The authors prepared pure maltulose by isomerizing maltose with alkali, hydrolyzing the unchanged maltose in the reaction mixture with amylo-glucosidase (gluco-amylase), chromatographing the resulting solution (consisting of glucose, maltulose and a small amount of fructose) on paper, and extracting the maltulose with water.
A paper entitled "Useful Properties of Maltose" by J. E. Hodge, J. A. Rendleman and E. C. Nelson, Cereal Science Today, Vol. 17, No. 7, July 1972, pgs. 180-188, presents a good discussion of the properties of maltose as well as other starch-derived sweeteners including maltulose. The authors prepared maltulose by chemical isomerization of maltose with sodium aluminate, and report 95% conversions by this method. The authors also report that, by "superficial testing" maltulose was judged sweeter than maltose but less sweet than sucrose or maltitol.
Sakai et al., in U.S. Pat. No. 3,691,013, rank the sweetness of a high maltulose product as about equal to maltitol, and below that of sucrose but above that of dextrose. The U.S. patent discloses the preparation of ketose sweetening agents having very high contents of maltulose (80% to 95%) plus small amounts of maltotriulose and other saccharides by subjecting a high-maltose hydrolyzate of starch to alkaline isomerization to convert a portion of the maltose to maltulose, converting the unreacted maltose to aldonic acid with a lactose dehydrogenase, and then removing the aldonic acids for formed. The patent also discloses the use of these very high maltulose products as sweetening agents in various food products.
U.S. Pat. No. 3,514,327 to Parrish discloses and claims a process for isomerizing glucose, maltose or lactose to the corresponding ketoses, i.e. levulose, maltulose and lactulose, respectively, by subjecting the aldose to the isomerizing action of certain specific amines.
Japanese published patent specification No. 49938/73 to Kikken Kagaku K. K. (published July 14, 1973, filed Oct. 27, 1971 as Japanese application No. 84655/71) shows isomerization of maltose in an aluminum-containing alkaline solution and very high conversions are reported. The three examples show the following products obtained by this isomerization technique: (1) 89.0% maltulose, 4.0% maltose, 1.5% levulose, 5.5% dextrose; (2) 74.1% maltulose, 0% maltose, 16.4% levulose, 9.5% dextrose; (3) 79.0% maltulose, 1.0% maltose, 12.7% levulose, 7.3% dextrose.
British Pat. No. 1,177,701 to Corn Products Company shows starch conversion syrups containing between 5% and 30% ketose (principally levulose), 35% to 45% dextrose and 15% to 35% maltose, prepared by treating a relatively high maltose starch hydrolyzate with glucoamylase to raise the dextrose content to at least 50% while retaining a substantial content of maltose, and then subjecting this hydrolyzate to an alkaline isomerization process to isomerize a portion of the dextrose to levulose. Although not specifically mentioned in the British patent, a small amount of maltulose is probably formed during the isomerization, in addition to the levulose.
In the area of maltulose the prior art workers have been principally concerned with obtaining pure maltulose (e.g. for experimental purposes) or end products having extremely high proportions of the sugar, i.e. 80% or higher, dry basis, in order to take maximum advantage of its sweetening power. My invention, on the other hand, comprises a new class of syrups, for use as sweeteners in food products, containing maltulose, dextrose and levulose, plus, optionally, maltose and/or higher saccharides (having degrees of polymerization greater than 2.)